The present invention relates generally to communication systems and, more particularly, to techniques and structures for the efficient use of packet data communications in radiocommunication systems.
The growth of commercial communication systems and, in particular, the explosive growth of cellular radiotelephone systems worldwide, has compelled system designers to search for ways to increase system capacity and flexibility without reducing communication quality beyond consumer tolerance thresholds. For example, most early cellular communication systems provided services using circuit-switched technologies. Now, however, mobile calls may be routed in a circuit-switched fashion, a packet-switched fashion, or some hybrid thereof. Moreover, it has become increasingly desirable to couple and integrate mobile cellular telephone networks, for instance a GSM network, to Internet protocol (IP) networks for call routing purposes. The routing of voice calls over IP networks is frequently termed xe2x80x9cvoice over IPxe2x80x9d or, more succinctly, VoIP.
Packet-switched technology, which may be connection-oriented (e.g., X.25) or xe2x80x9cconnectionlessxe2x80x9d as in IP, does not require the set-up and tear-down of a physical connection, which is a significant difference relative to circuit-switched technology. This feature of packet data typically reduces the data latency and increases the efficiency of a channel in handling relatively short, bursty, or interactive transactions. A connectionless packet-switched network distributes the routing functions to multiple routing sites, thereby avoiding possible traffic bottlenecks that could occur when using a central switching hub. Data is xe2x80x9cpacketizedxe2x80x9d with the appropriate end-system addressing and then transmitted in independent units along the data path. Intermediate systems, sometimes called xe2x80x9crouters,xe2x80x9d are stationed between the communicating end-systems to make decisions about the most appropriate route to take on a per packet basis. Routing decisions are based on a number of characteristics, including, for example: least-cost route or cost metric; capacity of the link; number of packets waiting for transmission; security requirements for the link; and intermediate system (node) operational status.
In packet data communication schemes, access to the system is provided on a random basis using a packet data scheduler disposed in the fixed part of the system. For example, a mobile station carries out a random access within a cellular digital packet data communication system in order to initiate a data transfer session. The random access can be carried out, however, only when the scheduler announces an idle time slot in the downlink. Then the mobile station initiates a transfer (for example by transmitting a BEGIN frame) in the idle time slot. When the cellular digital packet data communication system receives the transfer, it acknowledges receipt of the BEGIN frame to the specific mobile station. This acknowledgment indicates to the mobile station that the communication system had success in decoding the message that was sent over the random channel. If the cellular digital packet data communication system did not receive the initial transfer, due to, for example, a collision of packets received from several mobile stations attempting random access at the same time, then the mobiles will retry random access after waiting for some e.g., random, time period. Included in the Begin message, the mobile proposes a temporary address to be used for the data transaction, and within the successful acknowledgement from the communication system, the communication system explicitly confirms the address. Alternatively, the communication system may explicitly transfer another temporary address that shall be used by the mobile terminal. It will be appreciated by those skilled in the art that different mechanisms for assigning a temporary address can be used.
Once a mobile station has made a successful random access, and is therefore active, it is scheduled by the system to transfer packets on a radio channel. The scheduling of transmission resources by the system for the active mobile station provides the mobile station with a reserved access, as opposed to a random access. The scheduling can be carried out on basis of the mobile""s Quality of Service (QoS) or other widely known methods. With the introduction of new services or applications over packet data systems, for example real time (RT) services such as VoIP, there will be a large variety of Quality of Service (QoS) demands on the network. Certain users, for example, those utilizing real time voice applications will have a very high demand for the availability of transmission resources, whereas users, for example, who transmit short messages or electronic mail, will be satisfied with a lower availability of transmission resources.
For example, in a UMTS system, there are four proposed QoS classes: the conversational class; streaming class; interactive class; and background class. The main distinguishing factor between these classes is the sensitivity to delay of the traffic. Conversational class traffic is intended for traffic which is very delay sensitive while background class traffic is the most delay insensitive traffic class. Conversational and streaming classes are intended to be used to carry RT traffic flows and interactive and background classes are intended to be used to carry Internet applications (e.g., WWW, E-mail, Telnet, FTP, etc.).
In considering how to accommodate varying QoS requirements in packet data systems, a problem has arisen in that a mobile station, which has already established a medium access control (MAC) transaction with the system may suddenly need to send additional, high priority (i.e., hard time constraint) packets. Such information could, for example, be control information blocks or high QoS payload blocks that need to be transferred to the system rather rapidly, which time constraints may not be achievable using the existing MAC transaction, i.e., by waiting for the mobile station""s next reserved access. For example, the mobile station may be involved in a data transaction, e.g., accessing a web page over the Internet, and need to establish a voice connection at the same time.
Given the limited resources available in radiocommunication systems, the existing MAC transaction may not be able to service the new voice connection sufficiently rapidly to avoid unacceptable delay in transmitting voice information, which information is well known to be rather delay sensitive. For example, the packet scheduler in the system may not schedule a next reserved access for the mobile station""s data connection sufficiently rapidly to service the new voice connection. This problem is exacerbated by the fact that packet data implementations in radiocommunication systems typically only assign temporary packet data (MAC) addresses to mobiles after they make a successful random access request. Since packet data implementations in radiocommunication systems are address limited as compared with, for example, packet data implementations in wireless LAN systems, i.e., the number of available addresses in the MAC transport channel does not permit all users in a cell to be assigned a MAC address, these systems employ temporary MAC addresses which result in the scheduler typically reserving sufficient resources for a mobile station to transmit a limited amount of data, e.g., 50 bytes. For systems utilizing temporary MAC addresses assigned to currently active users, the overall performance may be damaged if unlimited access is given to the random access occasions, since the delay over the random access channel will increase based on the number of accesses made from the mobile users due to an increased number of collisions.
Accordingly, it would be desirable to provide systems and methods for providing enhanced mechanisms to more rapidly service mobile stations"" need to send data packets having hard time constraints and, in particular, for servicing those mobile stations that have existing packet data transactions. Moreover, it would be desirable to provide a more flexible packet data system which addresses the complex problem of having many mobile stations operating in a cell at the same time, each potentially running different applications having different QoS requirements and at the same time solving the problem of the limited bandwidth available for overhead communication and resource scheduling on the random access channel.
The present invention overcomes the above-identified deficiencies in the art by providing a method and system for packet data communications which permits flexible usage of both random access and reserved access opportunities for packet data transmission. According to exemplary embodiments of the present invention, a mobile station can use a random access opportunity to transmit a data packet even if it already has an existing data connection for which it is awaiting a reserved access opportunity. For example, if a mobile station has an existing data connection and that mobile station""s user initiates a voice connection, then the mobile station may use either a reserved access time slot or a random access time slot (whichever occurs first) to transmit the voice data packet. In this way, the present invention provides more rapid servicing of data packets having hard time constraints.
According to another exemplary embodiment of the present invention, the different random access opportunities may be assigned a priority such that a mobile station that wants to use a random access opportunity to transmit data can only use the random access opportunity if it has a priority level that is the same as, or higher than, that of the random access opportunity. For example, if random access opportunities are assigned one of two priority levels (high and low) and if a mobile station has a low priority level, then it can only use a random access opportunity having a low priority level. The priority level of a random access opportunity according to this exemplary embodiment can be indicated by assigning a first address to high priority random access opportunities and a second address to low priority random access opportunities. Then, the system can transmit either the first or second address indicating which type of random access opportunity is valid for the next uplink time slot. Of course, more than two priority levels may be implemented.
As an alternative to the foregoing, mobile stations can identify random access opportunities as having a particular priority level, without the access level being explicitly signaled by the system. For example, according to another exemplary embodiment of the present invention, a mobile station that is waiting for a next reserved access opportunity may receive an indication that a first random access opportunity is available. If the mobile station is, for example, a high priority mobile station, then it may use the first random access opportunity to transmit data. Otherwise, if it is a low priority mobile station, it continues to wait for its assigned reserved access opportunity. If, however, a second random access opportunity is signaled by the system then the low priority mobile station can use this second random access opportunity to transmit data. This technique can also be applied when the mobile station is making the initial random access, i.e., it has not received an address and is not waiting for its reserved access.